Ceramics and glasses are used in implantable medical devices for a variety of purposes. In some instances, optical windows including ceramics or glasses are used to transmit optical energy in vivo either into the device or out of the device to monitor or detect a variety of conditions or parameters. In other cases, optical windows including ceramics or glasses are used to provide an electrically insulated point of entry into the device for, e.g., a feedthrough pin used to deliver electrical signals or energy between the interior and exterior of the device.
When used for transmitting optical energy, it is important that the optical window assembly be capable of transmitting light of the desired wavelengths. One example of an implantable medical device using optical energy is a blood oxygen sensor. In some instances, the sensors are located along the lead of, e.g., a pacemaker. By incorporating a blood oxygen sensor into an implantable cardiac pacemaker, the patient's blood oxygen saturation level can be monitored and used as one factor in setting the pacemaker's rate.
Like any device designed for implantation, implantable medical devices incorporating optical windows must be made of biocompatible and biostable materials. In addition, devices must also be hermetically sealed to protect the components within the implantable device from contamination. In the case of a blood oxygen sensor designed for long-term placement in a blood environment, the design also preferably provides smooth outer surfaces to minimize the formation of clots and other undesirable events.
Attempts at providing optical transmission into and out of implantable medical devices such as blood oxygen sensors located in leads has included providing the optical sensors or sources enclosed in glass or sapphire tubes and other structures. Enclosing the devices within a tube presents a number of problems in the manufacture of such devices. In addition, it is often difficult to provide a long-term hermetic seal to prevent contamination of the devices by body fluids.
Where optical windows including ceramics or glasses are used to electrically insulate, e.g., a feedthrough pin, it is advantageous to use a window formed of material that is electrically non-conductive and that may also be optically transmissive. The optically transmissive characteristic can be useful because it allows for relatively easy visual inspection of the feedthrough assembly to determine whether any cracks are present in the lens (i.e., insulating) material that could compromise hermeticity of the device.
Although not admitted as prior art, examples of implantable medical devices incorporating optically transmissive portions, such as windows, etc., can be found in the published documents listed in Table 1 below.
______________________________________ Patent/Document No. Inventor(s) Issue/Publication Date ______________________________________ H1114 Schweitzer et al. December 1, 1992 B1 4,467,807 Bornzin June 30, 1992 3,746,087 Lavering et al. July 17, 1973 3,847,483 Shaw et al. November 12, 1974 4,114,604 Shaw et al. September 19, 1978 4,202,339 Wirtzfeld et al. May 13, 1980 4,399,820 Wirtzfeld et al. August 23, 1983 4,407,296 Anderson October 4, 1983 4,421,386 Podgorski December 20, 1983 4,444,498 Heinemann April 24, 1984 4,523,279 Sperinde et al. June 11, 1985 4,554,977 Fussell November 26, 1985 4,623,248 Sperinde November 18, 1986 4,651,741 Passafaro March 24, 1987 4,697,593 Evans et al. October 6, 1987 4,727,879 Liess et al. March 1, 1988 4,750,495 Moore et al. June 14, 1988 4,791,935 Baudino et al. December 20, 1988 4,807,629 Baudino et al. February 28, 1989 4,813,421 Baudino et al. March 21, 1989 4,815,469 Cohen et al. March 28, 1989 4,830,488 Heinze et al. May 16, 1989 4,903,701 Moore et al. February 27, 1990 5,005,573 Buchanan April 9, 1991 5,040,538 Mortazavi August 20, 1991 5,058,586 Heinze October 22, 1991 5,067,960 Grandjean November 26, 1991 5,113,862 Mortazavi May 19, 1992 5,176,138 Thacker January 5, 1993 5,267,564 Barcel et al. December 7, 1993 5,312,454 Roline et al. May 17, 1994 5,329,922 Atlee, III July 19, 1994 5,358,519 Grandjean October 25, 1994 5,411,532 Mortazavi May 2, 1995 5,438,987 Thacker et al. August 8, 1995 5,490,323 Thacker et al. February 13, 1996 5,535,752 Halperin et al. July 16, 1996 5,564,434 Halperin et al. October 15, 1996 WO 80/01620 Kraska et al. August 7, 1980 ______________________________________
All patents listed in Table 1 above are hereby incorporated by reference in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and Claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the teachings of the present invention.